Au interfaces with epitaxially grown CdTe(111): Chemistry and barrier heights

Abstract

We have used high-resolution soft x-ray photoemission spectroscopy (SXPS) to study chemistry, atomic distributions, and Fermi level (EF) movement caused by Au deposition on molecular beam epitaxy (MBE) -grown CdTe(111)-B surfaces. Using etch-and-anneal cycles, we produce clean surfaces with characteristic valence-band and core-level photoemission spectra. Au atoms disrupt substrate bonds releasing both Cd and Te atoms into the overlayer. Anions segregate preferentially to the free surface, while cations are more interspersed in the Au matrix. These first SXPS studies of CdTe(111) surfaces indicate that the atom-induced disruption is comparable or less than that for cleaved (110) substrates. After correcting for photovoltaic effects, we obtain an equilibrium Fermi-level position 0.55 eV above the valence-band maximum (Ev), intermediate between stabilization positions for Au on (i) cleaved, bulk-grown CdTe(110) (Ev+0.8 to 1.1 eV), and (ii) cleaved, bulk-grown CdTe(110) with a Yb interlayer (Ev+0.45 eV). Despite clear evidence for interfacial diffusion, EF for MBE-grown CdTe(111) lies closer to the position expected on the basis of work function difference than does EF for bulk-grown CdTe(110). These results indicate that the structural and electronic quality of the CdTe crystal plays a major role in the Schottky barrier formation.